1. Field of the Invention
The present invention relates to a method of forming a housing used in an inkjet head with high nozzle density and an inkjet recording device that includes the housing.
2. Related Art
FIG. 1 shows an example of a conventional inkjet recording device disclosed in Japanese Patent-Application Publication No. SHO-58-119872 that uses deformation of a piezoelectric element to apply pressure to ink in a pressure chamber so as to eject an ink droplet from a nozzle that is in fluid communication with the pressure chamber.
The inkjet recording head of FIG. 1 includes a channel plate, a reinforcement plate 206, piezoelectric elements 204, and feet 224. The channel plate is made from a nozzle plate 201, a chamber plate 220, and a diaphragm plate 310 stacked on top of each other. The chamber plate 220 is formed with pressure chambers 200, and the nozzle plate 201 is formed with orifices 202. Each foot 224 is provided to one end of a corresponding one of the piezoelectric elements 204. The reinforcement plate 206 has a higher rigidity than the channel plate and is provided to improve the inter-chamber rigidity of the chamber plate 220. The reinforcement plate 206 connects to the diaphragm plate 310 at positions between adjacent feet 224 and also guides movement of the feet 224. When one of the piezoelectric elements 204 deforms, the corresponding foot 224 moves vertically. This applies pressure to the ink in the corresponding pressure chamber 200 and ejects an ink droplet through the corresponding orifice 202. This type of head can be driven using a low voltage, can be produced with a fairly high nozzle density, and has excellent ejection characteristics. However, adjacent feet 224, and also adjacent piezoelectric elements 204, cannot be located too tightly together because the reinforcement plate 206 is interposed between adjacent feet 224. Because it has been difficult to form through holes, in which the feet 224 are inserted, in high density in the reinforcement plate 206, this configuration places limits on the nozzle density of the head.
FIG. 2 shows an inkjet recording head, disclosed in Japanese Patent-Application Publication No. HEI-6-8422, proposed for overcoming the above-described problem. The inkjet recording head of FIG. 2 includes a chamber plate 410 and a housing 412. The chamber plate 410 is formed with a row of pressure chambers 404. The housing 412 has greater rigidity than the chamber plate 410 and is formed with an opening 421 that extends in the same direction as the row of pressure chambers 404. A plurality of piezoelectric elements 402 are fixed to the chamber plate 410 at positions in the opening 421 that confront the pressure chambers 404. A fixing base 400 formed with a thin-film electrode 401 is attached to each piezoelectric element 402 so that a portion of the thin-film electrode 401 is in intimate contact with the corresponding piezoelectric element 402. A lead 403 is connected to an exposed surface of each thin-film electrode 401. When a voltage is supplied through the lead 403 to the corresponding piezoelectric element 402, the piezoelectric element 402 contracts in its lengthwise direction, that is, the direction indicated by an arrow Z in FIG. 2. When application of voltage is stopped, then the piezoelectric element 402 reverts to its initial state. Because no member is provided in between adjacent piezoelectric elements 402 for guiding the piezoelectric elements 402 in the configuration of FIG. 2, the piezoelectric elements 402 can be aligned in a much higher density than with the configuration of FIG. 1.
If the pressure chambers 404 are formed with a large width to ensure that ink droplets are sufficiently large, then the width of the opening 421 in the housing 412 must also be enlarged. This increases the cross-sectional surface area of the opening 421. Also, the recording head must be made longer in the nozzle row direction in order to increase the number of nozzles to increase print speed. This also increases the cross-sectional surface area of the opening 421.
However, the chamber plate 410 is extremely thin, that is, with a thickness of only about 0.8 mm to 1.0 mm. The section of the chamber plate 410 that is formed with the pressure chambers 404 has a total thickness of only about 0.4 mm to 0.6 mm. Accordingly, if the opening 421 of the housing 412 is too large, then deformation of any one of the piezoelectric elements 402 will deform the entire chamber plate 410 and not just the corresponding pressure chamber 404. The displacement generated by the piezoelectric elements 402 is not effectively used to eject ink droplets. Also, crosstalk can be generated between neighboring nozzles that reduces consistency in speed of ejected ink droplets or otherwise degrades ejection characteristic. Crosstalk can become particularly serious when a great number of piezoelectric elements 402 are driven simultaneously. When neighboring pressure chambers 404 are affected by the deformed simultaneously with a pressure chamber 404 that is driven to eject ink, the ink meniscus in nozzles corresponding to the neighboring pressure chambers 404 can vibrate.
Further, the center of the chamber plate 410 can be deformed by pressure applied by the piezoelectric elements 402 while the piezoelectric elements 402 are brought into attachment with the chamber plate 410 so as to fix the piezoelectric elements 402 to the chamber plate 410. This deformation can change the ejection characteristics at the nozzles near the center of the head to differ from those near the ends of the head.